The present invention relates to fuel injectors for use with internal combustion engines and particularly with diesel engines. More particularly, the present invention relates to hydraulically actuated fuel injectors.
Referring to the drawings, FIGS. 5 and 5a show a prior art fuel injector 350. The prior art fuel injector 350 is typically mounted to an engine block and injects a controlled pressurized volume of fuel into a combustion chamber (not shown). The prior art injector 350 of the present invention is typically used to inject diesel fuel into a compression ignition engine, although it is to be understood that the injector could also be used in a spark ignition engine or any other system that requires the injection of a fluid.
The fuel injector 350 has an injector housing 352 that is typically constructed from a plurality of individual parts. The housing 352 includes an outer casing 354 that contains block members 356, 358, and 360. The outer casing 354 has a fuel port 364 that is coupled to a fuel pressure chamber 366 by a fuel passage 368. A first check valve 370 is located within fuel passage 368 to prevent a reverse flow of fuel from the pressure chamber 366 to the fuel port 364. The pressure chamber 366 is coupled to a nozzle 372 through fuel passage 374. A second check valve 376 is located within the fuel passage 374 to prevent a reverse flow of fuel from the nozzle 372 to the pressure chamber 366.
The flow of fuel through the nozzle 372 is controlled by a needle valve 378 that is biased into a closed position by spring 380 located within a spring chamber 381. The needle valve 378 has a shoulder 382 above the location where the passage 374 enters the nozzle 378. When fuel flows into the passage 374 the pressure of the fuel applies a force on the shoulder 382. The shoulder force lifts the needle valve 378 away from the nozzle openings 372 and allows fuel to be discharged from the injector 350.
A passage 383 may be provided between the spring chamber 381 and the fuel-port 364 to drain any fuel that leaks into the chamber 381. The drain passage 383 prevents the build up of a hydrostatic pressure within the chamber 381 which could create a counteractive force on the needle valve 378 and degrade the performance of the injector 350.
The volume of the pressure chamber 366 is varied by an intensifier piston 384. The intensifier piston 384 extends through a bore 386 of block 360 and into a first intensifier chamber 388 located within an upper valve block 390. The piston 384 includes a shaft member 392 which has a shoulder 394 that is attached to a head member 396. The shoulder 394 is retained in position by clamp 398 that fits within a corresponding groove 400 in the head member 396. The head member 396 has a cavity which defines a second intensifier chamber 402.
The first intensifier chamber 388 is in fluid communication with a first intensifier passage 404 that extends through block 390. Likewise, the second intensifier chamber 402 is in fluid communication with a second intensifier passage 406.
The block 390 also has a supply working passage 408 that is in fluid communication with a supply working port 410. The supply port is typically coupled to a system that supplies a working fluid which is used to control the movement of the intensifier piston 384. The working fluid is typically a hydraulic fluid that circulates in a closed system separate from the fuel. Alternatively the fuel could also be used as the working fluid. Both the outer body 354 and block 390 have a number of outer grooves 412 which typically retain O-rings (not shown) that seal the injector 350 against the engine block. Additionally, block 362 and outer shell 354 may be sealed to block 390 by O-ring 414.
Block 360 has a passage 416 that is in fluid communication with the fuel port 364. The passage 416 allows any fuel that leaks from the pressure chamber 366 between the block bore 386 and piston 384 to be drained back into the fuel port 364. The passage 416 prevents fuel from leaking into the first intensifier chamber 388.
The flow of working fluid into the intensifier chambers 388 and 402 can be controlled by a four-way solenoid control valve 418. The control valve 418 has a spool 420 that moves within a valve housing 422. The valve housing 422 has openings connected to the passages 404, 406 and 408 and a drain port 424. The spool 420 has an inner chamber 426 and a pair of spool ports that can be coupled to the drain ports 424. The spool 420 also has an outer groove 432. The ends of the spool 420 have openings 434 which provide fluid communication between the inner chamber 426 and the valve chamber 434 of the housing 422. The openings 434 maintain the hydrostatic balance of the spool 420.
The valve spool 420 is moved between the first position shown in FIG. 5 and a second position shown in FIG. 5a by a first solenoid 438 and a second solenoid 440. The solenoids 438 and 440 are typically coupled to a controller which controls the operation of the injector. When the first solenoid 438 is energized, the spool 420 is pulled to the first position, wherein the first groove 432 allows the working fluid to flow from the supply working passage 408 into the first intensifier chamber 388 and the fluid flows from the second intensifier chamber 402 into the inner chamber 426 and out the drain port 424. When the second solenoid 440 is energized the spool 420 is pulled to the second position, wherein the first groove 432 provides fluid communication between the supply working passage 408 and the second intensifier chamber 402 and between the first intensifier chamber 388 and the drain port 424.
The groove 432 and passages 428 are preferably constructed so that the initial port is closed before the final port is opened. For example, when the spool 420 moves from the first position to the second position, the portion of the spool adjacent to the groove 432 initially blocks the first passage 404 before the passage 428 provides fluid communication between the first passage 404 and the drain port 424. Delaying the exposure of the ports reduces the pressure surges in the system and provides an injector 350 which has more predictable firing points on the fuel injection curve.
The spool 420 typically engages a pair of bearing surfaces 442 in the valve housing 422. Both the spool 420 and the housing 422 are preferably constructed from a magnetic material such as a hardened 52100 or 4140 steel, so that the hysteresis of the material will maintain the spool 420 in either the first or second position. The hysteresis allows the solenoids 438, 440 to be de-energized after the spool 420 is pulled into position. In this respect the control valve 418 operates in a digital manner, wherein the spool 420 is moved by a defined pulse that is provided to the appropriate solenoid 438, 440. Operating the control valve 418 in a digital manner reduces the heat generated by the solenoids 438, 440 and increases the reliability and life of the injector 350.
In operation, the first solenoid 438 is energized and pulls the spool 420 to the first position, so that the working fluid flows from the supply port 410 into the first intensifier chamber 388 and from the second intensifier chamber 402 into drain port 424. The flow of working fluid into the intensifier chamber 388 moves the piston 384 and increases the volume of chamber 366. The increase in the chamber 366 volume decreases the chamber pressure and draws fuel into the chamber 366 from the fuel port 364. Power to the first solenoid 438 is terminated when the spool 420 reaches the first position.
When the chamber 366 is filled with fuel, the second solenoid 440 is energized to pull the spool 420 into the second position. Power to the second solenoid 440 is terminated when the spool reaches the second position. The movement of the spool 420 allows working fluid to flow into the second intensifier chamber 402 from the supply port 410 and from the first intensifier chamber 388 into the drain port 424.
The head 396 of the intensifier piston 396 has an area much larger than the end of the piston 384, so that the pressure of the working fluid generates a force that pushes the intensifier piston 384 and reduces the volume of the pressure chamber 366. The stroking cycle of the intensifier piston 384 increases the pressure of the fuel within the pressure chamber 366. The pressurized fuel is discharged from the injector 350 through the nozzle opening 372. The actuating fluid is typically introduced to the injector at a pressure between 300-4000 psi. In the preferred embodiment, the piston has a head-to-end ratio of approximately 7:1, wherein the pressure of the fuel discharged by the injector is between 2,000-28,000 psi. The fuel is discharged from the injector nozzle openings 372 and the first solenoid 438 is again energized to pull the spool 420 to the first position and the cycle is repeated.
The prior art HEUI injection system 350 has a relatively quick rise of the injection pressure after initiation of the injection event. As the intensifier piston 384 travels downward under the influence of the actuating fluid, injection pressure builds up very quickly. Under higher actuation fluid pressure (oil pressure), the injection pressure build-up process is abrupt, due to high acceleration of the intensifier piston 384. With the high initial injection pressure of the HEUI injection system 350, the initial rate of the injection is also relatively high and hence contributes to higher NOx emission in an internal combustion engine. As is known, high NOx emission is undesirable as a pollutant. With stringent emission regulations currently being imposed, there is a need in the diesel engine industry to control the initial injection rate so that a gradual rise or rate-shaped injection rate profile can be obtained and the NOx emissions may be favorably affected.
U.S. Pat. No. 5,492,098 presents an invention which improves HEUI injection by adding a spill port at bottom of the plunger. With some spilling of the high pressure fuel at the beginning of the injection, initial injection pressure rises more slowly, hence producing a rate shaping feature. However, due to the spilling of high injection pressure fuel, significant energy is lost to the low pressure fuel reservoir. This loss can not be recovered during the injection event. Such high energy loss is not desirable. It would be advantageous to provide for rate shaping of the rate of fuel injection without significant loss of fuel pressure energy.
An objective of the present invention is to use a delay device to postpone or slow down the initial injection pressure build up while retaining high fuel pressure energy. With slow initial pressure rising in the injection nozzle chamber, rate shaping can be obtained and controllability of small pilot injection is improved.
Advantages of the present invention are as follows:
Placing a delay device between pressure generation chamber (plunger chamber) and nozzle chamber allows delay of the initial injection pressure rise and tailoring the amount of rate shaping before the main injection event commences. A slow and controllable fuel pressure rise during the initial portion of the injection event is very critical to the precision control of the initial small quantity fuel delivery, especially during a pilot injection mode. Such control further provides repeatability between injection events.
This delay device can be applied to any fuel injection system and specifically is not limited to the HEUI injection system.
The present invention is a delay device for use with a fuel injector, the fuel injector having an electric controller for controlling the flow of a high pressure actuating fluid responsive to initiation and cessation of a pulse width command, the pulse width command defining the duration of an injection event, and an intensifier being in fluid communication with the controller, the intensifier being translatable to increase the pressure of a volume of fuel for injection into the combustion chamber of an engine; the delay device includes an apparatus, shiftable between a first disposition and a second disposition over a certain period of time after initiation of the pulse width command, the period of time effecting a delay in initiation of fuel injection after initiation of the pulse width command. The present invention is further a fuel injector including a delay device. Additionally, the present invention is a method of controlling a fuel injection event, includes the steps of sending a pulse width command to a controller to define an injection event, flowing an actuating fluid from the controller to affect an intensifier responsive to reception of the pulse width command, pressurizing a volume of fuel by means of the intensifier, flowing a high pressure fuel from the intensifier to an injector nozzle, and interposing a delay in at least a portion of the flow of fuel to the injector nozzle.